Generally, tachometer assemblies are assembled to a rotating machine by first attaching the tachometer shaft to the machine rotor, and then securing the tachometer housing to the machine housing, or vice versa. In either case, a persistent problem exists, however, in those instances where the machine rotor is located at the bottom of a blind hole in the machine housing, since there is insufficient space to locate tools, such as wrenches and the like, which are otherwise used to affix the tachometer shaft to the rotor.
This invention solves the problem by incorporating an "internal wrench" into the tachometer assembly. By proper manipulation of the tachometer shaft, the latter may be locked to the tachometer housing in an installation mode so that the shaft can be screwed directly into a threaded bore in the rotor simply by rotating the entire tachometer assembly. Then, by further manipulation of the tachometer housing, the tachometer shaft can be released so that the tachometer housing can be secured to the machine housing, with the tachometer shaft free to rotate with the rotor in an operative mode.
In an exemplary embodiment of the invention, a tachometer assembly includes a main body and a cover which may be joined together to form the tachometer housing which encloses a PC board assembly, a sensor pad, and a rotatable shaft/drum assembly. The drum periphery has indicia thereon which are sensed by the sensor pad, from which signals are generated to provide an accurate reading of the rotation of the rotor or motor shaft (hereinafter referred to simply as "the" rotor for convenience) via its axial connection to the tachometer shaft. In accordance with this invention, the tachometer shaft and drum assembly may be pulled forwardly so that the shaft extends out of the main body of the tachometer a distance greater than normal to facilitate installation. In this extended position, also referred to herein as an installation mode, the tachometer shaft can be locked to the main body portion of the housing via an internal wrench mechanism, so that by rotating the tachometer housing, the tachometer shaft will rotate therewith. In this installation mode, the tachometer shaft may be properly aligned in the blind hole with a threaded bore in the rotor, and threadably engaged therewith via manual rotation of the tachometer housing itself which, of course, remains outside the blind hole. Once the tachometer shaft is fully threaded into the rotor, the tachometer shaft may be released to permit axial as well as rotational movement relative to the tachometer housing, so that the tachometer housing may be moved forwardly and fixedly secured to the motor housing, leaving the tachometer shaft free to rotate with the rotor.
In its broader aspects, therefore, the present invention relates to a tachometer assembly for attachment to an output shaft of a rotary machine, wherein the tachometer assembly includes a housing enclosing a sensor fixed to a tachometer shaft, the shaft extending from the tachometer housing adapted for attachment to the output shaft of the rotary machine for rotation therewith, and a sensor pad located peripherally adjacent the sensor, the improvement comprising an internal wrench means for locking the tachometer shaft to the tachometer housing for common rotation therewith so as to facilitate engagement between the tachometer shaft and the output shaft, and for unlocking the tachometer shaft from the tachometer housing for rotation relative to the tachometer housing to thereby permit the tachometer shaft to rotate with the output shaft after the tachometer housing is secured to the rotary machine housing.
In another aspect, the invention relates to a tachometer assembly for attachment to a rotor of a rotary machine comprising a tachometer housing enclosing a sensor and associated sensor pad, the sensor fixed to a tachometer shaft projecting from the tachometer housing, the shaft provided with a transverse drive pin engageable within a pair of recesses formed in the tachometer housing so as to releasably, rotationally and axially lock the tachometer shaft to the housing in an installation mode, the drive pin also disengageable from the pair of recesses so as to release the tachometer shaft for rotation relative to the tachometer housing in an operative mode.
The invention is thus seen to provide a simple solution to an otherwise difficult problem through the incorporation of an internal wrench into a tachometer assembly.